1. Field of the Invention
The present invention relates to a system, a method and the like for transferring multimedia data or the like from a delivery server to mobile communication equipment in a mobile communication system using a technique such as a mobile phone system, a PHS, a wireless LAN or the like.
2. Description of the Prior Art
In a mobile communication system using W-CDMA (Wideband Code Division Multiple Access), there is proposed a technique called “HSDPA (High Speed Downlink Packet Access)” for improving a speed of communication to mobile communication equipment (a terminal device), i.e., a downlink communication speed.
The HSDPA can realize high speed and high efficiency of downlink communication without a large change of technical specifications of W-CDMA. Although the downlink communication speed is 2 Mbps at most in the current W-CDMA, it can be improved up to approximately 14 Mbps by using HSDPA.
If HSDPA becomes commonplace in the future, it is predicted that services of delivering content including high resolution moving images that need a high bit rate will become widespread though it is difficult with the conventional technique.
In order to deliver content including high resolution moving images to mobile communication equipment by using HSDPA, there are following problems to be solved.
For the time being after starting a communication service by using HSDPA, cells where the communication service is available will increase gradually. Therefore, there will be mixed cells where the communication service is available and conventional cells.
Therefore, when a user moves from an HSDPA cell to a conventional cell, it may cause a situation where the mobile communication equipment cannot receive the content smoothly. In this case, the content may not be provided as the user wants.
Therefore, it is considered to use the method as described in PCT Application No. PCT/FI2003/000686 or No. PCT/FI2003/000752. According to the method described in PCT Application No. PCT/FI2003/000686, a data transmission bit rate from a streaming server is changed in accordance with a downlink communication speed.
According to the method described in PCT Application No. PCT/FI2003/000752, after reselection of a cell, a mobile client device requests a streaming server to resend streaming media that cannot be received due to the reselection of the cell.
However, the conventional method described in PCT Application No. PCT/FI2003/000686 or No. PCT/FI2003/000752 may increase a load on the streaming server since the request is issued to the streaming server. If the load on the streaming server becomes excessive, delivery of data cannot be performed smoothly.